Application of metal coatings by the seizure method

ABSTRACT

METAL COATINGS ARE APPLIED TO ARTICLE SURFACES BY FRICTIONAL CONTACT BETWEEN THE SURFACE AND A SCRIBER OF THE METAL TO BE DEPOSITED, THE METAL BEING A SPECIAL ALLOY OF ALUMINUM AND AT LEAST 0.1% BY WEIGHT OF AT LEAST ONE SECONDARY METAL GIVING THE ALLOY A BRINELL HARDNESS OF NOT MORE THAN 100.

v Oct. 24, 1972 E. PLUMAT 3,700,496

APPLICATION OF METAL COATINGS BY THE SEIZURE METHOD Filed April 29, 1970 INVENTOR Emile Plumor ATTORNEYS.

3,700,496 APPLICATION OF METAL COATINGS BY THE SEIZURE METHOD Emile Plumat, Gilly, Belgium, assignor to Glaverbel S.A., Brussels, Belgium Filed Apr. 29, 1970, Ser. No. 32,967 Claims priority, application Luxembourg, May 2, 1969, 58,564; Great Britain, Mar. 26, 1970, 14,891/ 70 Int. Cl. C23c 17/00; H05b 3/12 US. Cl. 117-211 14 Claims ABSTRACT OF THE DISCLOSURE Metal coatings are applied to article surfaces by frictional contact between the surface and a scriber of the metal to be deposited, the metal being a special alloy of aluminum and at least 0.1% by weight of at least one secondary metal giving the alloy a Brinell hardness of not more than 100.

BACKGROUND OF THE INVENTION This invention relates to the metallizing of surfaces of vitreous, vitrocrystalline and ceramic materials, and to articles of those materials having metallized surfaces.

It is known to metallize various materials by deposition of the metal in vacuo, by spraying the substrate material with molten metal or by applying to the substrate material liquids containing components which react to form a metal coating in situ. In industry, metallizing has sometimes to be performed in circumstances and under conditions in which none of these methods is entirely suitable, due possibly to economic factors or the difficulties of confining the coating metal to predetermined surface zones of a substrate.

Another method of metallizing a substrate which has special advantages ofits own is the so-called seizure method the essential characteristic of which is the transfer of metal to the substrate by friction between the substrate and a metallic scribing member which may, for example, be in the form of a disc rotated in contact with the substrate.

The simplicity of this latter method and the precise control of the metal deposition which it makes possible, makes the method of special potential interest in the production of certain metallized articles, e.g., glazing panels bearing metal coating strips capable of conveying electrical current for resistance heating purposes. However, when using the scribing members hitherto proposed, it has been found very difiicult to produce satisfactory, or consistently satisfactory, coatings on various glasses and vitrocrystalline materials unless the coatings are so thin as to have an electrical resistance above, and in most cases very considerably above, 0.5 ohm per square of any size. The friction' transfer of thicker metal deposits, even when it can be accomplished, necessitates the imposition of pressure and tangential forces of such magnitude as to involve a substantial risk of breaking or weakening the substrate, particularly in the case of sheets of glass of ordinary compositions as commonly used in vehicle windscreens.

SUMMARY OF THE INVENTION It is a primary object of the present invention to overcome these drawbacks and difficulties.

Another object of the invention is to facilitate the application of metal layers by the seizure method.

A further object of the invention is to provide an improved scribing member for applying such layers.

According to the present invention, the difficulties referred to above can be overcome by using a scribing member composed of an alloy selected from a range of United States Patent 0 Patented Oct. 24, 1972 aluminum alloys. A number of specific examples of suitable alloys Will be given hereafter. The invention is not however restricted to the use of those particular alloys. Once attention has been directed by this disclosure to the field of aluminum alloys it will be possible for those skilled in the art to find alloys other than those specified hereinafter, which permit the formation of coatings of lower electrical resistance than those hitherto formed by the seizure method.

Accordingly, the present invention includes any article having at least one surface portion of vitreous, vitrocrystalline or ceramic material, on which a coating of metal has been applied by the seizure method, characterized in that the coating is composed of an aluminum alloy and has a maximum resistance of 0.3 ohm per square.

Preferably the coating has a maximum resistance of 0.06 ohm per square.

The term vitrocrystalline as used herein denotes a material which has been formed by heat-treating a wholly vitreous material to produce one or more crystalline phases. The term ceramic denotes a refractory composition comprising a mass of crystals which have been formed into a coherent mass with or without a binder.

To determine whether or not a given metal coating has been applied by the seizure method it is only necessary to examine the substrate surface beneath the coating. Evidence of the practice of the seizure method sometimes takes the form of slight indentation of the substrate surface Where the coating metal has been applied, the indentation having been accompanied by local flow of the substrate material. In the case of many substrate materials coming Within the scope of the invention, and particularly in the case of ordinary soda-lime and other common types of glass, a surface coated by the seizure method will exhibit microabrasions. Such microabrasions do not materially lower the tensile strength of glass any more than the superficial scratches which almost inevitably appear during normal handling of glass products. The substrate surface should preferably be at least free of fissures or cracks which are large enough to be visible to the naked eye.

Generally speaking, it has been found that the fissures become dangerous for the mechanical strength when their gravity is such that they become visible. Acceptable and not visible fissures may be 0.7 mm. long, 30 microns deep I and have a width which cannot be distinguished by an optical microscope. Not acceptable and visible fissures either have larger sizes or are accumulated with a so strong density that shells appear.

In comparison with the present invention, glass surfaces to which metal has been frictionally transferred from prior art scribing members have "been found to either exhibit very high electrical resistance or possess visible fissures which substantially lower their tensile strength.

The preferred aluminum alloys, specified hereinafter, enable coatings to be formed which have a resistance of less than 0.3 ohm per square, and even less than 0.06 ohm per square.

The preferred alloys comprise aluminum and at least 0.1% by weight of a secondary metal or metals, a eutectic mixture of which, with aluminum, contains less than 20% by weight of such other metal, said alloy having a liquidus temperature not exceeding the melting temperature of the aluminum by more than 40 C. (thus not exceeding 700 C.), and having a maximum electrical resistivity of 4 microhm-cm. Alloys meeting these specifications can be very readily applied by the seizure method, particularly to ordinary glass, without subjecting the substrate to forces which would be harmful.

Advantageously, an aluminum-based alloy is used which has the above specifications and comprises at least one metal in the following group: antimony, bismuth, cadmium, indium, lead, tellurium and silicon. Aluminumbased alloys containing these secondary metals often.have

very satisfactory resistance to corrosion under the action of water in liquid or vapor form.

It has been found particularly advantageous to use an aluminum-based alloy containing 0.4-1.6% by weight of antimony or 2-10% by weight of silicon.

Very good results are obtainable by using alloys, which preferably, but not necessarily, have the specifications just defined, containing aluminum and a content of at least 0.1% by weight, based on the total weight of the alloy, of a secondary metal or metals, at least part of such content being dissolved in the aluminum and the rest, if any, being contained in a separate phase constituting less than 12% by weight of the alloy.

Advantageously, an aluminum-based alloy is used which has these latter specifications and comprises at least one metal selected from the following group: silver, copper, magnesium and zinc. These metals are soluble in the solid state in aluminum, in various amounts, on condition that cooling is carried out at suitable speeds from the solidus temperature down to a temperature which is near the room temperature. If too high a quantity of the secondary metal is in a separate phase this adversely affects the quality of the metal coating. Generally, it has been found that speeds of about 10 C. per minute allowed the obtainment of alloys which did not contain much metal in a separate phase; very high speeds (of about 600 C. per minute) and very slow speeds (of about 1 C. per minute) have generally resulted in non-satisfactory alloys. In any case, it is easy to adjust the cooling speed in such a way that an alloy of low separated phase( s) content is obtained.

It has been found particularly advantageous to use an aluminum-based alloy containing 2 to 5% by weight of ZlIlC.

Preferably the aluminum alloy used has a Brinell hardness of not more than 100. In the most preferred embodiments, the alloy used has a Brinell hardness of not more than 55.

It has been found advantageous for not more than 12% of the total alloy to be made up of one or more secondary phases, i.e., one or more phases other than the predominating phase consisting of or containing aluminum.

In the present specification a eutectic composition is considered to form a single phase even if it is not impossible to observe the coexistence of two different finegrained phases, under very considerable magnification. More particularly, when using a secondary metal which forms a eutectic mixture with aluminum, it is preferred to use the eutectic composition itself, so that the alloy consists of a single phase in the broad sense just referred to.

The invention particularly includes articles comprising a sheet of glass bearing a coating of aluminum alloy on at least one strip-like zone less than 2 mm. in width, the coating having a maximum resistance of not more than 0.3 ohm per square, and preferably not more than 0.06 ohm per square. Such a sheet has a transparency which is only slightly less than that of the sheet of glass prior to application of the coating. Moreover, the coating strip or strips has or have an attractive shiny appearance. The coating strip or strips enable the sheet to be appreciably heated by the passage of substantial electric currents. The coated sheets can be produced quite inexpensively and the coated glass sheets have a mechanical strength com parable with the strength of uncoated glass sheets which have been in use for some months.

The coating or coatings on an article according to the invention can be formed using a scribing member in the form of a body which has a circular profile and is mounted for rotation in contact with the body to be coated.

The invention includes methods of forming articles as hereinbefore defined.

The invention also includes aluminum alloys suitable for forming a coating as hereinbefore referred to, and particularly includes aluminum alloys suitable for that purpose and having one or more of the compositional features hereinbefore referred to, and the aluminum alloys specifically identified in this specification. The invention also includes scribing members, e.g., discs, formed of an aluminum alloy according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a vehicle window coated according to the invention.

FIG. 2 is an edge view of the window of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, a glazing 1 is formed by a sheet of thermally tempered ordinary soda-lime silica glass curved to form a vehicle rear window. Eight parallel linear-metal deposits 2, the outermost of which are indicated at 5, are produced by the rotation of a metal disc in contact with the glass accompanied by relative bodily displacement between the disc and the glass sheet to cause metal to transfer from the disc to the sheet along the indicated longitudinal lines. In a subsequent operation a coating of silver is formed on each of two end contact zones 3 by applying a suspension of metallic silver in benzene. The silver coatings have a fairly low resistance and serve to distribute electric current to the various conductive strips 2. Terminals 4 are soldered to the end zones 3 using an ordinary tin solder. The resulting rear window can be successfully heated by connecting the terminals 4 to a source of electric current.

FIG. 2 illustrates in simplified form a scriber disc 8 made of a material according to the invention. The disc 8 is supported and rotated by a motor 9 via a support and drive link 10 which could have any suitable form. In applying coating strips 2, the motor can be mounted on a stationary support and the glass sheet 1 can be carried by any type of carriage capable of moving the sheet past the disc 8 as the disc rotates about its axis.

The illustrated rear window and the method of forming the coating strips 2 are defined by the following data:

Length of strips: 1 m.

Width of strips: 0.8 mm.

Thickness of deposits: 5-10 microns Distance between strips: 30 mm.

Operating voltage: 12 volts Power dissipated in the central zone of the window: 600

Average resistance per strip: 18 ohms Resistance measured along various strip sections: 0.7-4

ohms/dm.

Calculated resistance of deposit per square: 5.6-32 milliohms Composition of the alloy of the disc (by weight): aluminum 98.9% approximately; antimony: 1.1%

Diameter of disc: mm.

Speed of rotation of disc: 200 rpm.

Pressure of disc on glass: 1 kg.

Speed of movement of glass beneath disc: 15-30 cm. per

minute A reduction in the electrical resistance per unit length of the strips can be obtained by using a thicker disc, in-

creasing the disc speed, increasing the pressure and/or reducing the speed of movement of the glass in relation to the disc. The electrical resistance per unit length of a strip is reduced by half when the speed of rotation of the disc is doubled. However, a thicker disc produces a wider deposit and this has the effect of reducing visibility through the rear window, whilst excessive pressure spoils the glass and may cause interruptions in the layer and result in a rapid misshaping of the disc.

If the rear window of a vehicle is to be adequately defrosted with a minimum consumption of electric power, it is advantageous for the greater amount of the power to be dissipated in the central zone of the glass so that it is advantageous for a deposit having a higher resistance to be produced in that region. To this end the speed of translational movement of the glass in contact with the disc may be higher during formation of the central portion of each strip than when forming the strip end portions. The variation in speed can be carried out stepwise or, preferably, continuously. Strips of different resistances can also be deposited; for instance the outermost strips can have a higher resistance than the other strips.

The formation of the coatings in the illustrated window do not materially reduce the mechanical strength of the thermally tempered glass sheet. In fact the mechanical strength immediately after formation of the metal deposits was close to that of an identical thermally tempered (but uncoated) window after a few weeks or months of use.

In a comparative test it was found that the mechanical strength of the glass is even less affected if the glass sheet is coated as in the previous example but using a disc scribing member made of the following alloy:

Percent by weight The conductive strips formed with this scribing member have substantially identical electrical properties to those in the previous example.

In forming the strip coatings by the seizure method as in the foregoing examples, in a few cases the glass substrate showed evidence of flow at the coatings lines, the surfaces of the glass being about 0.5-1.0 micron lower beneath the coatings than in the regions between coating strips.

As regards the alloys used in the above examples, it is known that a eutectic mixture of antimony and aluminum contains 1.1% by weight of antimony.

In regard to the second alloy, zinc can be in solid solution in aluminum at room temperature on condition that the alloy is cooled with suitable cooling speed from the solidus temperature. A suitable cooling speed is about C. per minute.

The alloys used in the above examples are sufficiently corrosion-resistant and their properties do not substantially deteriorate in use on a vehicle rear window.

Conductive metal strips having properties close to those of the strips formed in the above examples have been produced by the same method, using the following alloys:

Al 90%In 10% Al 90%Ag 10% Al 99.5%Sb 0.5%

The invention has uses apart from the manufacture of vehicle windows. Rcsistances for electrical applications can be made according to the invention and the substrate may bear the coating metal over its entire surface instead of on spaced zones. Linear deposits can, for example, be formed side by side or with a slight overlap, to form an all-over coating. The invention can be used for applying conductive coatings to form contact zones, like the zones 3 in FIG. 1, for feeding electric current to conductive coating strips which may also be applied according to the invention or by some other method, such as deposition in vacuo, for example. Other examples are ceramic or glass 6 bodies bearing aluminum alloy coatings formed preparatory to the making of ceramic-to-metal or glass-to-metal seals.

If desired, a deposit formed according to the invention can be coated over with a deposit of the same or some other composition, metallic or not, by any other method, for instance, by electrolysis or spraying.

The aluminum-based alloy deposits can be protected by anodic oxidation.

The following table gives data relating to four sheets of glass (denoted I-IV) each bearing an alloy coating along twelve strip-like linear zones 1 meter in length, 0.6 to 0.7 mm. in width and 10 to 15 microns in thickness, the zones being at a spacing of 30 mm. The coatings on each of the four sheets were applied from a disc scribing member having a diameter of mm. and a thickness of 0.5 mm. and the disc was rotated at 30 r.p.rn. and exerted a pressure of 3 kg. on the glass surface during each coating pass along the glass sheet, the speed of such pass being 0.6 meter/min. Four difierent scribing discs were used: a different one for each sheet of glass. The table gives the compositions of the aluminum alloys forming the different discs and data relating to the electrical properties of the alloy coatings on the sheets:,

TAB LE 1 II III IV Alloy composition (in percentages by weight):

Si 0. 9-1 Mg 0. 9-1 Fe 0. 5 8b-... 1. I Zn 4. 0 Al. 1 Electrical propert s of coat Electrical resistance of each coating strip in ohms 4. 5 12.0 13. 2 23. 7 Aggregate electrical resistance of parallel coating strips O. 375 1.0 1. 1 1. 97 Power output in watts (at 14 volts). 520 196 178 100 Resistance per square (in milliohms) 2.9 7. 8 8. 6 15. 4 Total current in amps (at 14 volts) 37 14 12. 7 7. 1

1 The rest.

In addition to the specific alloys mentioned in the specification all alloys which have been tested and which satisfy the general conditions set forth herein (Le. having a Brinell hardness of not greater than 100, having a second metal concentration of greater than 0.1%, and including a second metal which either: forms an eutectic mixture containing less than 20% of the second metal, the alloy having a liquidus temperature of not more than 700 C. and a maximum resistivity of 4 microhmcm.; or is dissolved in the aluminum and is present in a separate phase constituting less than 12% by weight of the alloy) have been found to produce coatings which achieve the objects of the invention.

It will be understood that the above description of the present invention is suspceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. An article having at least one surface portion composed of a vitreous, vitrocrystalline or ceramic material and carrying on such surface portion a coating of a metal applied by the seizure method, the metal comprising an alloy composed of aluminum and at least 0.1% by weight of a substance constituted by at least one of silicon and at least one second metal, the substance being of a type which forms a eutectic mixture with aluminum containing less than 20% by weight of such substance, said alloy having a liquidus temperature not exceeding the melting temperature of pure aluminum by more than 40 C. and having a maximum resistivity of 4 microhm-cm., and said coating having a maximum resistance of 0.3 ohm per square.

2. An article as defined in claim 1 wherein said second metal is selected from the group consisting of: antimony, bismuth, cadmium, indium, lead and tellurium.

3. An article as defined in claim 1 wherein said substance is antimony and is present in said alloy in a concentration of 0.4 to 1.6% by weight.

4. An article as defined in claim 1 wherein said substance is silicon and is present in said alloy in a concentration of between 2 and 10% by weight.

5. An article as defined in claim 1 wherein said coating has a maximum resistance of 0.06 ohm per square.

6. An article as defined in claim 5 wherein the surface portion of the material on which the coating is applied exhibits a depression and the surface of the depression shows evidence of flow due to the coating operation.

7. An article as defined in claim 6 wherein the surface portion on which a coating is applied is free from cracks which are visible to the naked eye.

8. An article as defined in claim 1 wherein the surface portion on which the coating is applied presents microabrasions beneath the coating.

9. An article as defined in claim 1 wherein said alloy is further composed of at least 0.1% by weight of at least one further metal, at least part of said further metal being dissolved in the aluminum and any remainder of the further metal being present in a separate phase which constitutes less than 12% by weight of the alloy.

10. An article as defined in claim 9 wherein the second metal is selected from the group consisting of antimony, bismuth, cadmium, indium, lead and tellurium, and the further metal is selected from the group consisting of silver, copper, magnesium andzinc.

11. An article having at least one surface portion composed of a vitreous, vitrocrystalline or ceramic material and provided with a metal coating applied to such surface portion by the seizure method, said coating being composed of an alloy comprising aluminum and at; least 0.1% by weight of at least one second metal, at least part of said second metal being dissolved in the aluminum and any remainder of the second metal being present in a separate phase which constitutes less than 12% by weight of the alloy, and said coating having a maximum. resistance of 0.3 ohm per square.

12. An article as defined in claim 11 wherein the second metal is selected from the group consisting of: silver, copper, magnesium and zinc.

13. An article as defined in claim 11 wherein the second metal is zinc and is present in the alloy in a concentration of between 2 and 5% by weight.

14. An article having at least one surface portion composed of a vitreous, vitrocrystalline or ceramic material and a metal coating applied to such surface portion by the seizure method, the coating metal being constituted by an alloy composed of aluminum and at least one second metal and having a Brinell hardness of not more than 100, the coating having a maximum resistance of 0.3 ohm per square.

References Cited UNITED STATES PATENTS 527,210 10/1894 Margot 117--124 C 1,157,569 10/1915 Moench 117-124 C X 1,982,774 12/ 1934 Winlder et al. 117-160 R X 3,117,886 1/1964 Glynn 117124 C X 3,256,109 6/1966 Berger 117-160 R X 3,265,520 8/1966 Obenshain 117-160 R X 2,667,431 1/ 1954 Burnside 117124 C X 2,780,708 2/1957 Glynn et al. 338308 X 3,288,983 11/1966 Lear, Sr. 2l9203 X 3,627,577 12/1971 Steidel 338-308 X FOREIGN PATENTS 1,364,604 5/1964 France 117D'IG 1 ALFRED L. LEAVlTT, Primary Examiner J. R. BATIEN, JR., Assistant Examiner U.S. Cl. X.R.

117-124 C, R, 212, 227, 229, DIG 1; 219203; -338'308 

